The present invention relates to disk circuits and, more particularly, to a method and apparatus for reading information from a magnetic disk.
Conventional magnetic storage devices include a magnetic transducer or xe2x80x9cheadxe2x80x9d suspended in close proximity to a recording medium, for example a magnetic disk, having a plurality of concentric tracks. The transducer is supported by an air-bearing slider mounted to a flexible suspension. The suspension, in turn, is attached to a positioning actuator. During normal operation, relative motion is provided between the head and the recording medium as the actuator dynamically positions the head over the desired track. The relative movement provides an air flow along the surface of the slider facing the medium, creating a lifting force. The lifting force is counterbalanced by a predetermined suspension load so that the slider is supported on a cushion of air. Air flow enters the xe2x80x9cleadingxe2x80x9d end of the slider and exits from the xe2x80x9ctrailingxe2x80x9d end. This air is used to prevent the head from contacting the disk, resulting in damage.
Writing data is typically performed by applying a current to the coil of the head so that a magnetic field is induced in an adjacent magnetic permeable core, with the core transmitting a magnetic signal across any spacing and protecting coating of the disk to magnetize a small pattern or digital bit of the medium within the disk. Reading of the information in the disk is performed by sensing the change in magnetic field of the core as the transducer passes over the bits in the disk. The changing magnetic field induces a voltage or current in the inductively coupled coil. Alternatively, reading of the information may be accomplished by employing a magneto-resistive (MR) sensor, which has a resistance that varies as a function of the magnetic field adjacent to the sensor. In order to increase the amplitude and resolution in reading the bits, the MR sensor is typically positioned on the slider as close to the disk as possible. Connected to these heads or sensors are read circuits which amplify the recorded data and eliminate noise. However, recently, some manufacturers of these MR sensors have switched from MR heads which employ a constant current source to MR heads which employ a constant voltage source. Consequently, there is a need for a read circuit which provides a constant voltage source instead of a constant current source. Thus, a constant voltage source would be desirable to be placed directly across the RMR, namely the resistance of the MR head. This aspect is especially true in that a need is required for a differential read circuit which provides a constant voltage source.
The present invention includes a constant voltage circuit which reads information from a head and which provides a constant voltage source for a differential amplifier. This constant voltage source is used instead of a constant current source and, consequently, the constant voltage source is placed directly across the resistance of the magneto-resistive sensor. Additionally, it is desirable to have such a constant voltage circuit which uses a feedback loop in order to provide the constant voltage. This feedback loop should be programmable so that different target values for the voltage drop across the resistance is achievable.